The use of optical glass fiber waveguides as a desired means for transmitting data has continued to grow in popularity. Fiber optic linkages have a very high information carrying capacity for their relatively small cross-sectional size, particularly in comparison to metal conductor wires.
The small size and fragile nature of the optical glass fibers make them very difficult to handle, however. Furthermore, the large number of virtually identical individual fibers present in most such installations makes fiber connection and splicing almost impossible without some assistance in fiber identification.
It therefore would be most desirable if individual optical fibers could be color coded, such as in accordance with the standard telecommunications color code as metal conductor wires typically are. This would permit ready and accurate identification of the individual optical glass fibers encountered in various applications. Unfortunately, up to now, various difficulties have prevented optical glass fiber waveguides from readily being supplied in such color coded form.
For example, it has not proven satisfactory to use conventional solvent based colorants, such as dyes, marking fluids, inks and the like, for color coding optical glass fiber waveguides, since such colorants lack acceptable compatibility with and adhesion to the protective coatings typically present on optical glass fiber waveguides and usually do not have long term resistance to the oils and gels encountered in cable installations. Solventbased colorants are also easily worn away by the physical abrasion typically encountered in cabling. Furthermore, such materials contain environmentally undesirable solvents and are difficult to apply with sufficient precision to leave a truly uniform coating about the circumference of the optical fiber. As far as the application of liquid solvent inks is concerned, conventional ink application apparatus and techniques are unsuitable for processing the fragile optical fibers.
As stated above, optical glass fibers are very fragile and easily subject to damages. Typically, therefore, they are coated with one or several protective plastic coatings as are discussed in U.S. Pat. Nos. 4,125,644 and 4,344,669. These protective coatings are applied as soon as the fibers are formed to protect against abrasion during takeup and handling.
It has been stated in U.S. Pat. No. 4,125,644 that various additives including pigments may be added to these protective plastic coatings, if desired. Thus to some degree coloration of the exterior of the fiber by coloration of the protective coating may be accomplished by the fiber producer to assist him in identifying particular products. However, as noted in U.S. Pat. No. 4,125,644, the type and quantities of substances added to the buffer coatings must be selected with care to avoid disturbing the desired qualities of the coatings. Also, the addition of pigment additives to the buffer coatings slows down the drawing and curing of the fibers and overall fiber production speed. These limitations restrict the extent of buffer coloration possible or desirable and preclude the feasibility of attaining full spectrum coloration of buffer coatings of all types as would be necessary to effectively color code and identify individual fibers.
Furthermore, in the production of optical fiber cables, it is important that the physical and optical characteristics of the fiber waveguides in the cable be carefully matched, and it is often desirable that all of the fiber waveguides be from the same production run or lot. Thus, even though it may be known that colorants can be added to the buffer coatings, as noted above, it is not feasible for the fiber producer to attempt to color code the fibers for fiber identification purposes by this method.